<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    function Un() {
        var instance;
        Un = function () {
            return instance;
        };
        Un.prototype = this;
        instance = new Un();
        instance.constructor = Un;

        instance.num = 10;
        instance.bang = 'big';

        return instance;
    }

    var u = new Un();
    var n = new Un();
    console.log(u === n);

    Un.prototype.hello = 'hello';
    console.log(u.hello);
    console.log(n.hello);

    console.log(u);
</script>
</html>